Many people (in this economy, especially)..
...wish to buy things that they do not have the funds to buy. (I apologize for the preceding overly obvious statement.)
When people get more money they spend some of it on things they would not have purchased otherwise. (Again, I apologize for stating the obvious.)
Demand for a product goes up as more people want to buy it. (I apologize for the preceding tautology!)
When demand for a product increases the producers of that product hire more staff. Also, people looking for a new business to start, usually consider starting one to produce a produce a product for which demand increases. (This is such simple stuff, I am embarrassed to state it!)